1. Field of the Invention
The present invention relates generally to the field of integrated circuit testing. More specifically, the present invention relates to a method and apparatus for improving the utilization of memory in integrated circuit testing systems.
2. Description of Related Art
Due to the high complexity of current semiconductor integrated circuits (ICs), testing of integrated circuits on automated test equipment (ATE) to detect manufacturing defects is a highly complex and costly task. Testing of each manufactured integrated circuit before it is shipped to a customer is essential, however, because a significant percentage of fabricated integrated circuits contain manufacturing defects, especially in case of large-scale integrated circuits fabricated using a state-of-the art manufacturing technology. Therefore, it is imperative to screen these defective chips out before they are shipped to a customer.
Today's ATEs test integrated circuits by applying the test patterns stored in the ATE memory to the IC under test and comparing the chip response to the expected response. In normal operation, ATEs apply a few bits of data to each input pin of the IC under test during every tester cycle. With current integrated circuits operating at clock cycles of hundreds of megahertz or gigahertz, a tester can potentially apply hundreds of millions of bits of data per chip pin within a second. However, ATE memory is a precious resource, and even a tester memory of 128 million bits per chip-pin is currently above the capacity of most available ATEs. ATE memory is expensive, because it needs to be a very high speed memory, and it is tied to the specific architecture of a particular ATE vendor. Moreover, an ATE typically has support for up to 512 chip pins via 512 separate ATE channels, and the associated ATE memory must be provided for every tester channel on the ATE. Therefore, it is crucial to utilize the tester memory as efficiently as possible while generating the test patterns to be stored in and applied by the ATE.